With recent broad acceptance of chemical toner technology in electrophotography, toner particle size in use is becoming dramatically small. Intuitively speaking, smaller toner size enables many printing advantages such as higher image resolution, less toner usage, faster fusing, etc. Surprisingly, however, there is little direct and systematic data in the literature.As an initial step to build a robust database of the particle size effects on EP performance, especially, of chemical toner, spherical polyester toner particles with five different (volume) average diameters (4.5, 5.8, 6.8, 7.8 and 8.8 microns) were prepared using chemical milling process and an identical external additive formulation was applied to prepare the toner compositions. Their physical characteristics (charging, fusing, particle flow, etc.) were determined. Also, their printing performance characteristics such as color intensity, image uniformity, image defects, toner consumption, etc. were determined using a HP CP1215 printer. The results are then to be interpreted in terms of expanded surface area of smaller size toner.